Electric fuse



March 1.2, 1929. R. w. GREGORY ET AL ELECTRIC FUSE Filed May 8, 1925 Patented Mar. 12, 1929.

UNITED STATES PATENT OFFICE. l

RICHARD WALTER GREGORY, OF HEXHAM-ON-TYNE, AND LEWIS COLIN GRANT, OF NEWCASTLE-UPON-TYNE, ENGLAND, ASSIG-NORS TO ELECTRICAL IMPROVEMENTS LIMITED, OF NEWCASTLE-`U'IOl\T-IYNEJ ENGLAND, A BRITISH COMPANY.

ELECTRIC FUSE.

Application filed May 8, 1925, Serial No. 28,941, and in Great Britain April 1, 1925.

This invention relates to electric fuses and has more particular reference to fuses for use in high voltage circuits as for example for connecting a power station busbar system to a potential transformer.

Such fuses are subjected to heavy currents under short-circuit conditions and in practice difficulty experienced in providing a fuse of such a nature as to clear the shortcircuit satisfactorily whilst the destructive effect is' limited to the fusible element only.

One known method of dealing with this difficulty is to employ an external resistance .in series with the fuse for the purpose of limiting the short-circuit current within the safe rating of the fuse. This arrangement can be made to operate satisfactorily but only if the resistance is heavy and large and consequently expensive to construct and diflicult to house safely.

The object of the present invention is to provide a pract-icable fuse .suitable for use on high voltage or other circuits in the form of a comparatively small self-contained unit.

In the fuse according to this invention a limiting resistance is connected in series with a fuse wire and is so constructed and arranged that it will exert force upon the fuse wire tending to sever it. Thus the arrangement is conveniently such that when the fuse blows the resistance will act to pull one end of the severed fuse wire away from the other. Preferably the lii'niting resistance is in the foi-1n of a holically coiled spring connected to one end ofthe fuse wire, and is so arranged that the electr-mnagnetic effect of current flowing through it will assist the force exerted by the spring.

A preferred construction according to the invention is illustrated by way of example in the accompanying drawings, in which Figure 1 is a central longitudinal section, and

Figures 2 and 3 are transverse sections on the lines 9.-2 and 3 3 respectively of Figure 1.

In this construction the fuse is contained within a tubular container A closed at one end by a conducting cap B. The other end of the container A is closed by means of an insulating` cap C around which is a further cap of conducting material D. This outer conducting cap D is electrically connected through the insulating cap C to one end of a short length of fuse wire E. Between the other end of the fuse wire E and the conducting' cap B at the far end of the container A is a helical spring F of nichrome or other resistance material. This spring F is connected in series with the fuse wire E and acts as a limiting resistance. The conducting caps B and D at the ends of the cont iner A are suitably faced as at B1 and D1 to form contacts for the external connection of the fuse to the circuit to be protected, the arrangementpreferably being such that when the fuse is in circuit there is no strain on the container' tube A.

The space around the fuse wire E and the spring F within the container may be filled with insulating material chosen to suit the conditions under which the fuse is to be used. Thus for example the whole container may be filled with oil or calcium carbonate, or again the fuse wire may be surrounded with a filling of calcium carbonate, whilst the space around the spring is air-filled. It will generally be desirable to provide a shaped insulating body Gr at each end of the fuse wire E to act as an arc deflector. The insulating cap C at the end of the container A adjacent to the fuse wire E is provided for the purpose of preventing an internal flash in case of rupture of the container tube.

When no current is flowing, the spring F exerts a force on the fuse wire E to maintain it in tension. This force is increased when a current flows owing to the electromagnetic effect of the current flowing through the turns of the spring` F. If a short-circuit current flows through the fuse, the fuse wire E will blow and the spring F will immediately pull the free end of the severed wire away from the other end under the joint action of the tension of the spring and the very large electromagnetic force. The spring F preferably has a large number of turns so to increase the electromagnetic action. Thus for example for a fuse rated for use on a 6,000 volt potential transformer when working under short-circuit conditions, the spring will have several thousand ampere-turns contributing to the electromagnetic effect. Moreover the spring acts as a limiting resistance and keeps the fusing current to a safe value, thus ensuring the localization of the destructive effect entirely within the container. The whole fuse unit is of light construction and can easily be housed within the switchgear cubicle, or

analogous housing commonly provided for fuses on switchgear or other apparatus.

What We claim as our invention end desire to secure by Letters Patent is l. In an electric fuse, the combination with :L fuse Wire, of a yielding member conn ct d to Said Wire and exerting` a force on the Wire tendirrg` to sever it, said member serving` to conduct current to the fuse Wire having such e resistance as to limit the current Within the safe of the Wire.

2. In en electricv fuse, the combination with a fuse wire, of :i tensiening member arranged in series With the Wire and exerting e iorce on the Wire tending to Sever it, said tensioning member having such e resistance es to limit the current Within the safe rating of the fuse Wire. e

3. 1n an electric fuse, the combination Witl e fuse Wire, of a spring associated therewith for conducting current to said Wire and for exerting a tension force thereon, seid spring constituting a resistance of Such an olimic fuse Wire disposed Within the'centeiner neer v one end thereof, a lielically coiled spring of conducting material connee Wl series with the fuse Wire within the container and eifering such resistance to the passe 'e oi' current es to limit the current ,vitliin the Seite rating' of the fuse, end @zips for eiorind he ende of the container7 means .seeming the YAfree end of the fuse Wire to the adjacent end cap whereby it can be electrically connected to en external circuit, sind ineens fer securing the free end of the Sprino to its adjacent end Cmp whereby it can be electrically ecnnerted to the external circuit.

B1 testimony whereof We names to this specification.

RCHARD XVALTER GREGORY. LETNIS COLIN GR@ Y have si gned our 

